The present invention relates to the field of fluid treatment plants, more particularly of the pressure swing adsorption type, comprising at least one compression machine for making fluids flow in the plant.
Compression machines, which create a pressure differential between an intake port and a delivery port and can therefore be used as a compressor for taking the fluid to a higher pressure or as a pump for sucking in the fluid and depressurizing an upstream circuit, are generally designed according to the desired inlet/outlet pressure difference or pressure ratio in normal operating conditions, the latter being manifested by a certain number of operational parameters for the compression machine, in particular the temperature of the moving parts. The clearances of the latter with respect to the stator and to the bearings take into account the expansion of these various components resulting from the temperature rise between the machine at rest and the machine in normal operation.
For low overpressures, typically of the order of 1 bar for operation as a compressor and of the order of 0.5 bar for operation as a vacuum pump, most compression machines, and especially rotating machines having profiled rotors, may operate without cooling, the expansion remaining moderate.
For higher overpressures and for extended operating periods, compression machines must be cooled by injecting cold gas or water into the fluid circuit.
Although providing enhanced performance and safety, cooled compression machines turn out to be particularly expensive, especially because of the ancillary equipment necessary.
Consequently, cooling proves to be necessary only for prolonged use with high compression ratios and it is possible to obviate the need for cooling by controlling and limiting the time for which the machine is operating at full speed according to pre-established charts, as described for example in the operating manual for Rootsxe2x80x94Hibonxe2x80x94Series SC superchargers, March 1993, sold by the company Hibon International.
However, controlling and running such a compression machine only according to the duration of operating phases at full speed is tricky to implement in plants varying in speed depending on the demand, with short treatment cycles, in which the compression and/or pumping phases are extremely short, or else in plants operating with a reversible compression machine, such as that described in document EP-A-0 743 087 in the name of the Applicant.
The subject of the present invention is a method of intermittently operating and of controlling a fluid compression machine coupled to a fluid treatment plant, typically of the pressure swing adsorption type, of simple and effective design, offering, including for uncooled machines, great operating flexibility and enhanced safety.
To do this, according to one characteristic of the invention, while the compression machine is operating, at least one clearance between two parts in relative motion of the latter is measured and the operation of the plant is varied according to this measurement.
According to more particular characteristics, a clearance measurement signal is generated, this signal is compared with a predetermined threshold and the operation of the plant is varied when the signal temporarily exceeds the threshold. In particular, for plants of the pressure swing adsorption type, all or part of the adsorption of the desorption cycle is varied.
Clearance measurements in compression machines, especially rotating machines, are well known in the art, as described for example in documents U.S. Pat. Nos. 5,198,763 and 5,696,444.
However, the aim of the known clearance measurements is essentially to monitor the change in clearances which change slowly and permanently, particularly as the parts in relative motion wear out, in order to eventually emit an alarm and/or stop the machine and not to operate a continuous process for regulating the operation of the gas treatment plant according to the present invention.
The subject of the invention is also a fluid treatment plant comprising at least one fluid compression machine, more particularly of the type not cooled by an external fluid, comprising at least one moving part in a stator in order to inject a fluid into at least one region of the plant and/or to extract a fluid therefrom, in which the compression machine comprises at least one detector which detects clearance between one region of the moving part and the stator and delivers a signal, and a control device which varies the operation of the plant in response to the signal.
Finally, the subject of the present invention is the application of such a plant to the production of a constituent of air, typically by retention of the other constituents of air on one or more adsorbent beds.